The second messenger cAMP regulates the expression of distinct subsets of genes in a variety of cell functions. The goal of this proposal is to test the hypothesis that cAMP-mediated gene expression is regulated by a protein complex containing both co-activators and co-repressors. This model of gene activation is an extension of the current model of gene regulation that involves distinct co-activator and co- represser complexes, where the components of these complexes are discrete and mutually exclusive. Our preliminary data show that CBP, the co-activator of the CRE-binding protein CREB, forms a complex with co-repressor histone deacetylases (HDAC). Our model proposes that CREB, when phosphorylated by Protein Kinase A, recruits CBP, which in turn brings HDACs to the CREB/CBP complex. We have shown that CREB is acetylated within the cell, and that acetylation of CREB enhances CREB's transactivation activity. Because CBP is a known histone acetyltransferase(HAT) and is able to acetylate CREB, we hypothesize that acetylation of CREB is regulated by the complex consisting of CBP and HDACs. The experiments proposed in this application focus on understanding the mechanism by which acetylation of CREB regulates its activity and the role of HDACs in regulating CREB acetylation. The CREB/CBP system has served as a prototype to illustrate the effects of phosphorylation of transcription factors and their interaction with co-activators/co-repressors on regulation of gene expression. Knowledge and insights gained from the proposed studies will have important implications for understanding the role of acetylation of transcription factors in the regulation of gene transcription.